This invention relates generally to the ozonation of various pool systems and, more particularly, to such treatment for the inactivation of cryptosporidium and reduction of chlorine concentrations. The treatment processes described herein provide unexpected and surprising results when compared to treatment systems of the prior art.
Swimming pool water differs significantly from drinking water, although almost universally potable water is used to fill pools, initially. Most state health codes for pools mandate a pH between 7.2 and 7.8. In addition, many of those codes also stipulate a minimum, and sometimes a maximum, level for a sanitizer, and recommend values for calcium hardness and bicarbonate alkalinity. The only sanitizers currently permitted are hypochlorous acid, HOCl (customarily referred to as chlorine in the pool industry), and less often hypobromous acid, HOBr (likewise, referred to as bromine). Any future use of xe2x80x9cchlorinexe2x80x9d or xe2x80x9cbrominexe2x80x9d herein refers to these acids, and not to the elemental forms of chlorine gas (Cl2) or liquid bromine (Br2).
With the exception of dichloro-isocyanuric acid, all compounds that produce chlorine or bromine in pool water influence the pH. It is therefore necessary to add either an acidic or caustic substance to maintain the pH. This means that pools have two injection systems: one for the selected sanitizer, and another one for the pH control.
The hypochlorous acid, often referred to as xe2x80x9cfree chlorine,xe2x80x9d can combine with ammonium ions in the water to form monochloramine (NH2Cl), and to a much lesser degree dichloramine (NHCl2). These chloramines are the main source of irritation for pool patrons, because they have a strong chlorine-like odor, and cause the typical xe2x80x9cswimmer""s red eyexe2x80x9d and itching. While a pool with a concentration of several mg/L chlorine is essentially odor-free, chloramine levels as low as 0.1-0.2 mg/L are noticeable.
Although chloramines are assumed to be the major contaminant fraction, it is known that other chlorinated amines may be present, such other chloramines including the chlorinated byproducts of creatine and creatinine (together, xe2x80x9ctotal chlorinexe2x80x9d). Chemical tests are available to measure the concentrations of free chlorine (HOCl), and xe2x80x9ctotal chlorine.xe2x80x9d The difference between these two measurements is called xe2x80x9ccombined chlorine,xe2x80x9d and is assumed to consist mostly of monochloramine. Although the various chlorinated nitrogen compounds have quite different properties, they are lumped together by the pool industry under the xe2x80x9ccombined chlorinexe2x80x9d label, mostly because the pool-side test kits cannot distinguish between the various chlorination byproducts. Most of the odor, and the eye and skin irritation at indoor pools is, however, directly related to the presence of mono- and di-chloramines.
Many state codes require -operators to initiate procedures such as breakpoint chlorination or the addition of high doses of non-chlorine oxidants, once the combined chlorine level reaches 0.5 mg/L. Breakpoint chlorination is a very slow process, and is usually done after hours or overnight. This means that the operator must start the process after the pool closes, and dechlorinate down to normal levels before the pool re-opens. Pool operators and owners have been looking for ways to reduce or eliminate this costly and labor-intensive procedure.
It should be noted that the chloramine problem is essentially limited to indoor pools. The natural air convection at outdoor pools, coupled with the volatility of the chloramines, ensures that outdoor pools rarely encounter problems with high levels of combined chlorine. Moreover, the tendency towards energy conservation has lead to drastically lowering the amount of fresh air drawn into indoor pool enclosures, and warm air rejected from there to the atmosphere. Elaborate humidity control and heat recovery systems ensure energy savings, but inhibit the venting of the odorous chloramines.
The requirement for maintaining chlorine levels at or above the specified minima is meant to ensure that the pool water remains free of harmful microorganisms. Bacteria, such as E. coli or Pseudomonas aeruginosa, that may be found in pool or hot whirlpool environments are easily inactivated when the required sanitizer level is continuously maintained. Exceptions are Giardia and Cryptosporidium, which are difficult to inactivate in a pool environment. Since the 1993 Crypto outbreak (drinking water) in Milwaukee, Wis., there have been a number of similar instances relating to swimming pools in Wisconsin, elsewhere, as well as waterparks in Georgia and California. Chlorine has an estimated CT-value of 9600 mg-min/L (where C is average concentration and T is average time) at typical pool water temperatures. With such high concentrations and/or time, it is clear that chlorine is completely ineffective in providing inactivation within a reasonable time span, and at levels tolerable to the bathers.
Ozone has a long history in the treatment of drinking water. However, its use in pool water treatment is much more recent, becoming common in Europe only during the 1960""s. The first large US pool ozone system is probably the German DIN-based system at the Peck Aquatic Facility in Milwaukee, Wis. Since then, the number of installed pool ozonation systems has increased rapidly. Most of these systems are, however, fairly small when compared to those required by European codes, such as the German DIN 19623. The typical US installation ozonates a side stream after the filter, with some units treating only 8%-10% of the total filtration flow, and others recommending 25% side stream ozonation for 4 minutes at 0.4 mg/L.
There are a considerable number of problems and deficiencies associated with pool water treatment systems of the prior art. There is a demonstrated need for an efficient, economical system by which pathologic microorganisms are reliably inactivated and noxious chlorine concentrations safely reduced.
Accordingly, it is an object of the present invention to provide a system and/or method for the ozonation of pool water volumes, thereby overcoming various deficiencies and shortcomings of the prior art, including those outlined above. It will be understood by those skilled in the art that one or more aspects of this invention can meet certain objectives, while one or more other aspects can meet certain other objectives. Each objective may not apply equally, in all instances, to every aspect of the present invention. As such, the following objects can be viewed in the alternative with respect to any one aspect of the present invention.
It is an object of the present invention to provide a pool treatment system whereby reduced levels of ozone can be used effectively to achieve various sanitation and/or oxidation effects.
It can be another object of the present invention to provide a method of ozone treatment of various pool water systems, so as to minimize problems associated with removal of excess ozone.
It can be another object of the present invention to provide an ozonation method and system configuration for use therewith to maximize filtration efficiency.
It can also be an object of the present invention to provide one or more methods for ozone treatment whereby higher average ozone concentrations are maintained over the course of treatment, to enhance effect and increase cost efficiency.
Other objects, features, benefits and advantages of the present invention will be apparent in this summary and descriptions of preferred embodiments, and will be readily apparent to those skilled in the art having knowledge of various water treatment systems. Such objects, features, benefits and advantages will be apparent from the above as taken in conjunction with the accompanying examples, tables, data and all reasonable inferences to be drawn therefrom.
In part, the present invention is a method of using ozone to meet CT values for the inactivation of the cryptosporidium microorganism/bacteria. The method includes (1) providing a pool filtration system, a total filtration flow volume with the system including a contact vessel and a filter downstream; (2) introducing ozone to the filtration flow volume prior to contact with the vessel, such that the ozone is introduced at an average concentration C, where C can preferably be but is not limited to an average concentration of about 0.5 mg/L to about 1.2 mg/L of water volume; and (3) contacting the filtration flow/water volume with said ozone for a time T sufficient and/or to provide a CT-value sufficient to inactivate the microorganism/bacteria. The contact vessel has a length and volume commensurate with the total filtration flow volume. The volume and length of such a vessel is predetermined to provide sufficient contact time with the ozone concentration. In preferred embodiments, the contact time is directly related to the flow rate of the water volume through the contact vessel. In preferred embodiments, the flow rate is less than about one inch of contact vessel length per second.
In part, the present invention also includes a method of reducing combined chlorine concentrations, in pool water, below threshold levels. The inventive method precludes the need for breakpoint chlorination, but includes (1) providing a pool filtration system with a total filtration flow volume, the system including a contact vessel and a filter downstream; (2) diverting about 1% to about 99% of the filtration volume; (3) introducing ozone to the diverted, partial filtration flow volume during pool operation and prior to contact with the vessel, with an ozone concentration of about 0.5 mg/mL to about 1.2 mg/mL of reduced water volume; (4) contacting the reduced water volume for a time sufficient with the ozone concentration; and (5) recombining the contacted, reduced water volume with the filtration flow volume.
With preferred embodiments, the partial volume of water diverted from the filtration flow is about 30% to about 50% of the total filtration flow volume. Regardless, the partial flow volume has a contact time with the vessel of about two minutes to about four minutes. In highly preferred embodiments, the contact vessel has a length and volume such that the flow rate of the reduced water volume through the contact vessel is less than about one inch of vessel length per second.
Even so, further ozone contact can be provided within the downstream filter after a recombination of water volumes. As a result, the combined chlorine concentration is less than about 0.5 mg/L.
In part, the present invention is also a method of oxidizing chloramines in pool water. The method includes (1) providing a pool filtration system with a total filtration flow volume, the system including a contact vessel and a filter downstream; (2) diverting part of the water volume from the filtration flow; (3) introducing ozone to the partial flow volume prior to the contact vessel, the water volume reduced to between about 1% and about 99% of the total filtration volume, and the ozone introduced at a concentration up to about the saturation point of ozone in the reduced water volume; (4) contacting the reduced water volume with the ozone; and (5) recombining the contacted, reduced water volume with the filtration flow volume. As described more fully above, in preferred embodiments, the partial flow volume is about 30% to about 50% of the total filtration flow. Contact with ozone can also occur within the downstream filter. A benefit of the present invention is, if required, introduction of ozone and subsequent oxidation during pool operation.
In part, as evident from the foregoing and various figures provided herewith, the present invention can also include in a pool filtration system having 1) a filter and associated filter flow; 2) a partial filter flow diverted from the filter flow; and 3) an ozonation system incorporated with the partial filter flow, such that the filter is downstream from the ozonation system. The partial filter flow can be between about 1% and about 99% of the filter flow, but is preferably between about 30% to about 50% thereof. Regardless, various preferred embodiments include a partial filter flow diverted from the filter flow upstream from the filter. Various other preferred embodiments include a partial filter flow diverted from the filter flow downstream from the filter. Optionally, the filtration system of this invention can further include a contact vessel included as a component of the ozonation system. Within or without the context of the preceding, a preferred contact vessel has a length and volume sufficient to provide a partial filter flow contact time of about 2 minutes to about 4 minutes.
Ozone is the strongest oxidant available for water treatment, and is also an excellent disinfectant. It has not experienced widespread use even though it would appear well-suited for chloramine destruction and inactivation of Crypto. Preliminary laboratory investigations show the destruction of monochloramine by ozone to be a very slow reaction. Tests at a number of pools suggest high dosages of applied ozone and contact times of 2 minutes or more are required to compensate for the slow destruction and eventually lower chloramine levels and keep them within acceptable levels.
Research since the forementioned Crypto episode indicates that ozonation appears to be the only feasible process for inactivation of the pathogen. However, this research was limited to temperatures encountered in drinking water treatment, from 0.5xc2x0 C. to a maximum of 25xc2x0 C. Most pools operate at higher water temperatures xe2x88x9228xc2x0 C. to 30xc2x0 C. for pools, and up to 40xc2x0 C. for hot whirlpools. The CT-value for Crypto at typical pool temperatures is estimated to be in about 3 mg-min/L. However, this estimate is based on initial theoretical ozone concentration values, neglecting the fact that under practical use situations, there are limits to ozone solubility and that such initial concentrations steadily decrease over time.
The inventive methodology described herein provides a route to the reduction and/or destruction of various chlorine species in treated pool water. The same general methodology also provides a heretofore unexplored avenue by which microorganisms can be rendered inactive. As a result, harmful microorganisms not otherwise treatable can be inactivated during the course of normal pool filtration. The examples and descriptions which follow illustrate how variations on the inventive methodology can be used to both sanitize pool water and reduce the problems associated with chlorination.